This invention relates to an optical illumination system which can efficiently irradiate light upon a light valve (display device) such as, for example, a liquid crystal display panel and a projection apparatus which includes an optical illumination system of the type mentioned.
Recently, display apparatus such as a projector apparatus, a television receiver and a display unit for a computer which use, for example, an optical element such as a liquid crystal display panel which is a light valve have been popularized in wide fields.
Such a projection apparatus which uses a liquid crystal display panel as described above spectrally decomposes light emitted from a light source into lights of the primary colors and introduces the lights of the primary colors into the liquid crystal display panel. The liquid crystal display panel optically modulates the lights of the primary colors with a video signal inputted thereto and composes the modulated lights of the primary colors to produce a color video signal.
The color video signal is projected in an enlarged scale onto a screen through a projecting lens.
In an optical system of such display apparatus as described above, an ultra high pressure mercury lamp, a metal halide lamp and so forth are used frequently as a light source due to their favorable color rendering properties.
The light sources mentioned, however, do not form an ideal point source of light and emit a luminous flux which has a large divergence angle.
Meanwhile, it is demanded that an illumination optical system used for an optical system to which the present invention is applied can irradiate a luminous flux emitted from a light source upon a liquid crystal display panel efficiently and uniformly.
However, a luminous flux generated by a light source used popularly has a large divergence angle as described above.
Therefore, it is difficult for a luminous flux emitted from the light source to be irradiated efficiently upon the liquid crystal display panel.
As means for causing a luminous flux emitted from a light source and having a large divergence angle in this manner to be irradiated efficiently upon a liquid crystal display panel, it is conventionally known, for example, to use a lens array having a structure which includes a large number of small lenses arranged in a grid-like arrangement or a like element to converge a luminous flux to reach the liquid crystal display panel with a uniform illuminance distribution.
An example of a typical projection apparatus which uses a lens array of the type described above is described below with reference to FIG. 1.
A light source 3 includes, for example, an ultra high pressure mercury lamp 3b disposed at a focal position of a paraboloid mirror 3a and emits a luminous flux having a predetermined convergence angle through an aperture thereof.
Of the luminous flux emitted from the light source 3, unnecessary rays of light in an infrared region (IR) and an ultraviolet region (UV) are intercepted by an UV/IR cut filter 5 while only effective rays of light are introduced into a first optical block 1 positioned rearwardly of the aperture of the light source 3.
The first optical block 1 is composed of an optical element including a first lens array 21 on which a plurality of convex cell lenses 21a having an outer profile substantially similar to an aspect ratio of effective apertures of liquid crystal display panels 45, 49 and 53 as light valves (optical spatial modulation elements) are arranged in a grid-like arrangement.
A second lens array 23 of a second optical block 2 disposed rearwardly of the first optical block 1 has a plurality of convex cell lenses 23a formed on the incoming side thereof and has a single convex surface 23f formed on the outgoing side thereof and serving as a first condensing component.
A pair of dichroic mirrors 14 and 27 for decomposing light emitted from the light source 3 into color lights of red, green and blue are disposed between the second lens array 23 and the effective apertures of the liquid crystal display panels 45, 49 and 53.
In the arrangement shown in FIG. 1, the red light R is reflected by the dichroic mirror 14 while the green light G and the blue light B are transmitted through the dichroic mirror 14. The red light R reflected by the dichroic mirror 14 has an advancing direction which is bent by 90 degrees by a mirror 15, and is then converged by a condensing lens 51 and introduced into the liquid crystal display panel 53 for red.
Meanwhile, the green light G and the blue light B having been transmitted through the dichroic mirror 14 are decomposed by the dichroic mirror 27. In particular, the green light G is reflected by the dichroic mirror 27 so that its advancing direction is bent by 90 degrees, and is introduced into the liquid crystal display panel 49 for green through a condensing lens 47. Meanwhile, the blue light B is transmitted through the dichroic mirror 27 and advances straightforwardly, and is introduced into the liquid crystal display panel 45 for blue by relay lenses 29 and 33, a condensing lens 43 and mirrors 31 and 35.
A polarizing plate (not shown) for polarizing incoming light to a fixed polarization direction is disposed on the incoming side of each of the liquid crystal display panels 45, 49 and 53, and another polarizing plate (not shown) which only transmits outgoing light having a predetermined polarization plane is disposed rearwardly of each of the liquid crystal display panels 45, 49 and 53. Each of the liquid crystal display panels 45, 49 and 53 thus modulates the intensity of light with a voltage of a circuit for driving liquid crystal.
The lights of the colors optically modulated by the liquid crystal display panels 45, 49 and 53 are composed by a dichroic prism 41 serving as optical composing means. The dichroic prism 41 reflects, with its reflecting face 41a, the red light R and reflects, with its reflecting face 41b, the blue light B both toward a projection lens 13.
Meanwhile, the green light G is transmitted through the reflecting faces 41a and 41b. Consequently, the red light R, green light G and blue light B are composed into a single luminous flux on an optical axis and projected in an enlarged scale to a screen 102 by the projection lens 13.
Now, a configuration of the lens arrays 21 of the first optical block 1 and the lens arrays 23 of the go second optical block 2 is described in more detail with reference to FIGS. 2 and 3.
First, FIG. 2 illustrates an example of formation of a luminous flux principally by an optical characteristic of the first optical block 1. A luminous flux L emitted from a light source is decomposed by the individual cell lenses 21a of the first lens array 21 and forms, after it goes out from the first optical block 1, images corresponding to the cell lenses 21a of the first lens array 21 in the proximity of the second optical block 2. Thereafter, the luminous flux is introduced into the condensing lens 47, which serves as a second condensing component, by the convex surface 23f of the second lens array 23. An image of the light source is reformed in the proximity of the pupil of the projection lens 13 shown in FIG. 1 by the condensing lens 47.
It is to be noted that reference numerals 41 and 49 denote a dichroic prism and a crystal display panel, respectively.
FIG. 3 illustrates an example of formation of a luminous flux by the second optical block 2. The divergence angle xcex8 with which a luminous flux can be taken in by the illumination system is controlled by suitably setting the outer profile dimensions of the cell lenses 23a and the distance between the first lens array 21 and the second lens array 23.
The thus taken in luminous flux within the divergence angle is introduced into the condensing lens 47, which serves as a second condensing component, by the convex surface 23f which serves as a first light condensing component. Consequently, the composed condensed light components composed from the first condensing component and the second condensing component are irradiated efficiently and uniformly upon the liquid crystal display panel 49 by the condensing lens 47.
The luminous flux emitted, for example, from a light source and introduced into the condensing lens 47 which serves as a second condensing component as described above is modulated by the liquid crystal display panel 49 having polarizing plates on the front and the rear thereof. Then, the modulated luminous flux is introduced into a color composing element such as, for example, the dichroic prism 41.
It is to be noted that the light which passes through the convex surface 23f serving as a first condensing component and is inputted to the condensing lens 47 serving as a second condensing component is the green light G of the light which has been decomposed intermediately into the red light R, green light G and blue light B by the optical element such as a dichroic mirror not shown as described hereinabove.
The dichroic prism 41 shown in FIG. 1 is formed from four prisms which are adhered to each other at reflecting faces 41a and 41b thereof, each of which is formed from a thin film having a predetermined reflection characteristic.
In FIGS. 1 and 2, only an optical path of the green light G is indicated by a sold line. Meanwhile, the red light R and the blue light B are introduced into the dichroic prism 41 from different directions from each other as indicated by arrow marks after they are optically modulated similarly by the liquid crystal display panels for the respective colors.
The green light G modulated by the liquid crystal display panel 49 is transmitted as it is through the dichroic prism 41, and the red light R introduced to the dichroic prism 41 is reflected by the reflecting face 41a while the blue light B introduced to the reflecting face 41b is reflected by the reflecting face 41b. In other words, the red light R, green light G and blue light B are composed by the dichroic prism 41 into a color video signal, which is introduced into the projection lens 13.
Since the first and second lens arrays 21 and 23 on which the convex cell lenses 21a and 23a are arranged in a grid-like arrangement are provided rearwardly of the light source in this manner, light emitted from the light source can be irradiated more efficiently and more uniformly upon the effective aperture of the liquid crystal display panel 45 (49, 53) than where only a condenser lens is disposed.
FIGS. 4A and 4B show an example of aspect ratios (ratio between the horizontal length and the vertical length) of the cell lenses 21a to 21d of the first lens array 21 and the cell lenses 23a, 23b, 23c and 23d of the second lens array 23. The aspect ratios are set, for example, 16:9. The aspect ratio of the cell lenses 21a, 21b, 21c and 21d is substantially equal to the aspect ratios of the liquid crystal display panels 45, 49 and 53 of FIG. 1 which are light valves and the aspect ratio of the screen 102 of FIG. 1.
Now, a relationship among the divergence angle with which a luminous flux can be taken in, the distance between the first and second lens arrays and the cell lens size of the second lens array is described with reference to FIG. 5.
Where the size of the cell lenses 23a of the second lens array 23 is represented by y and the distance between the first and second lens arrays is represented by 1 as seen in FIG. 5, the convergence angle xcex8 with which a luminous flux can be taken in is given by Tan xcex8=y/l. Where only the first and second lens arrays are provided in this manner, the divergence angle with which a luminous flux can be taken in depends only upon the distance between the first and second lens arrays and the cell lens size y of the second lens array.
In order to cause light emitted from the light source to be irradiated efficiently upon a liquid crystal display panel 45, a polarization conversion system is used popularly.
FIG. 6 shows an illumination optical system when a polarization conversion system 60 is used.
Referring to FIG. 6, light emitted from the light source 3 passes through the first optical block 1 formed from the first lens array and is irradiated upon the polarization conversion system 60, whereafter it is outputted toward the condensing lens 47 by the second optical block 2 which is formed from the second lens array.
The polarization conversion system 60 includes, as hereinafter described, a polarizing beam splitter, a reflecting face, and a xcex/2 plate for converting the polarization direction of light. When light emitted from a light source and having random polarization planes is introduced at a predetermined angle to the polarizing beam splitter, P polarized light waves are transmitted through the polarizing beam splitter while S polarized light waves are reflected to the direction of the optical axis again by the reflecting face so that they thereafter advance along the optical axis. By disposing a xcex/2 plate on only one of the optical paths of the thus decomposed P polarized light and S polarized light, the polarization plane of only one of the P polarized light and the S polarized light can be rotated, and consequently, the polarization planes of all of the P polarized light and the S polarized light can be made coincide with each other.
The light outputted from the polarization conversion system 60 and having the uniform polarization plane is irradiated upon the liquid crystal display panel 49. Consequently, light emitted from the light source can be irradiated efficiently upon the liquid crystal display panel by making most of such light components which have conventionally been absorbed by a polarizing plate.
As the location of the polarization conversion system 60, it may be disposed between the light source and the first optical block, in the proximity of the second optical block 2, or the like. Preferably, however, the polarization conversion system 60 is disposed in the proximity of the second optical block 2 from a point of view of the utilization efficiency of light as seen in FIG. 6.
In an illumination optical system wherein such an ultra high pressure mercury lamp, a metal halide lamp or the like as described above is used as a light source, in order to efficiently utilize a luminous flux emitted from a light source, it is necessary to efficiently take in a luminous flux of a predetermined divergence angle of a lamp.
Such taking in of a luminous flux of the divergence angle is controlled by the distance between the first lens array and the second lens array and the size of the cell lenses of the second lens array as described above.
However, in order to efficiently utilize a luminous flux emitted from the light source, it is necessary to dispose the polarization conversion system 60 described above in the proximity of the second lens array as shown in FIG. 6. As a result, a plurality of aperture limits are produced in the proximity of the second lens array as seen in FIGS. 7A to 7C, and the convergence angle with which a luminous flux can be taken in is limited. Further, since S polarized light which is reflected by the polarizing beam splitter of the polarization conversion system has an optical path which is bent by the polarizing beam splitter and the reflecting face, the optical path length of the S polarized light is longer than the optical path length of P polarized light which is transmitted through the polarizing beam splitter. This provides a difference in divergence angle with which a luminous flux can be taken in between the P polarized light path and the S polarized light path. As a result, a luminous flux of a sufficient divergence angle cannot taken in with one of the P polarized light path and the S polarized light path. This deteriorates the light utilization efficiency of the optical system.
This is described more particularly with reference to FIGS. 7A to 7C.
If the polarization conversion system 60 is disposed in front of a cell lens 23a of the second lens array, then the size of the cell lens 23a becomes one half that of a cell lens 21a of the first lens array as seen in FIGS. 7A to 7C. Further, a plurality of apertures are produced by the polarization conversion system 60 in addition to the aperture of the cell lens 23a of the second lens array, and the divergence angle with which a luminous flux can be taken in is limited by the plurality of apertures.
For example, if the image forming position f of the cell lens of the first lens array is set on the aperture which is closest to the first lens array, then only a luminous flux of a region A from within a luminous flux of a divergence angle xcex81 inputted to a maximum aperture can be transmitted through the optical system as seen in FIG. 7A.
Then, if the image forming position f of the cell lens of the first lens array is set on the aperture which is positioned closest to the liquid crystal display panel, then only luminous fluxes in regions B and C from within a luminous flux of a divergence angle xcex82 inputted to the maximum aperture can be transmitted through the optical system as seen in FIG. 7B.
Further, also where the optical path of the polarization conversion system 60 is shorter as in FIG. 7C, if the image forming position of the cell lens of the first lens array is provided nearer to the liquid crystal panel, then light in the region A from within light whose divergence angle is greater than xcex83 cannot still be transmitted through the polarization conversion system 60.
In the illumination optical system which uses only part of a luminous flux which is transmitted through the first lens array in this manner, color irregularity occurs on the liquid crystal display panel from irregularity of illuminance on the liquid crystal display panel or unevenness of an incoming ray of light to the dichroic mirror disposed adjacent the first condensing component with respect to the liquid crystal display panel. Consequently, the luminous flux which can be utilized effectively is that luminous flux which can be transmitted through the entire face of the first lens array and can be transmitted through the polarization conversion system and the second lens array.
It is an object of the present invention to provide an optical illumination system and a projection apparatus wherein light can be irradiated efficiently upon a display device such as, for example, a liquid crystal display panel.
In the optical illumination system of the present invention, a luminous flux from a light source is irradiated upon a light valve, which forms a display apparatus, through an optical apparatus for illumination.
A first optical block of the optical apparatus for illumination includes a first lens array.
The first lens array has a plurality of cell lenses having a substantially similar shape to that of the light valve.
A second optical block has a second lens array and a polarization conversion system. The second lens array has a plurality of cell lenses and corresponds to the first lens array of the first optical block.
A first condensing component of the second optical block condenses a luminous flux having been transmitted through the second lens array toward the light valve.
A second condensing component is disposed in the proximity of the light valve in order to form an image of a luminous flux outputted from the second optical block at a predetermined position.
In this instance, where the optical path length of a shorter one of optical paths of P polarized light and S polarized light decomposed by the polarization conversion system is represented by S and the optical path length of a longer one of the optical paths is represented by L, the image forming position f of the first lens array is set so as to satisfy
S less than f less than L
Consequently, in such an optical system as described above, a luminous flux of a possible maximum divergence angle can be taken in, and also the difference in divergence angle between the S polarized light path and the P polarized light path can be reduced. Consequently, a luminous flux emitted from the light source can be utilized effectively.
With the optical illumination system, since the focal position f of the first lens array positioned adjacent the light source is set so as to satisfy S less than f less than L, the divergence angle from the light source can be increased, and consequently, there is an advantage that a uniform image forming performance can be obtained while preventing loss or irregularity of the light amount.
The above and other objects, features and advantages of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings in which like parts or elements denoted by like reference symbols.